The present invention generally relates to ultrasound imaging. In particular, the present invention relates to banding suppression in ultrasound imaging.
Ultrasound is sound having a frequency that is higher than a normal person may hear. Ultrasound imaging utilizes ultrasound waves or vibrations in the frequency spectrum above normal human hearing, such as the 2.5-MHz range. Ultrasound imaging systems transmit ultrasound into a subject, such as a patient, in short bursts. Echoes are reflected back to the system from the subject. Diagnostic images may be produced from the echoes. Ultrasound imaging techniques are similar to those used in SONAR and RADAR.
B-mode (brightness mode) imaging is a grayscale ultrasound imaging technique that constructs images based on echoes received from pulses transmitted through a cross-section of the subject scanned. In B-mode imaging, the brightness of a spot or pixel representing an echo in a grayscale image corresponds to the strength of the received echo. The voltage of an echo received at an ultrasound receiver is an indication of brightness. B-mode imaging may be used on its own or combined with Doppler imaging or another imaging technique.
Forming the best possible image at all times for different anatomies and patient types is important to diagnostic imaging systems. Poor image quality may prevent reliable analysis of the image. For example, a decrease in image contrast quality may yield an unreliable image that is not usable clinically. Additionally, the advent of real-time imaging systems has increased the importance of generating clear, high quality images. Differences between different body types may result in blurring, streaking, or introduction of ghost images or artifacts in a resulting image. Automatic optimization of diagnostic images helps to ensure consistent image quality over a wide range of patients.
Multiple focal zones are often used to improve resolution and/or penetration of an ultrasound image. A focal zone is a location within the body at which the transmitted ultrasound pulse is focused. Each focal zone has a corresponding focal region over which energy transmitted to that focal zone produces the best image. Typically, different waveforms and/or f-numbers (a ratio of lens focal length to lens aperture diameter) are used for different focal zones, and the focal region includes the focal zone. When multiple focal zones are used, an ultrasound image is formed by adjoining each focal region that corresponds to the focal zones. When two or more regions are joined together, the borders of the regions may be distinct and visible in the image. The artifactual edges are known as banding artifacts. Banding artifacts are caused by differences in speckle brightness or texture between two focal regions. Currently, transmit waveforms and depth-dependent gain curves are carefully selected to eliminate banding artifacts on the average patient. However, patient body types are diverse (particularly with pathology), and banding artifacts may occur despite the most carefully selected gain curves. Therefore, a real-time, adaptive band-suppression method is needed to reduce banding artifacts over a wide range of patient body types.
Thus, an ultrasound imaging system that automatically adjusts system parameters in real time to reduce banding on a wide range of patient body types would be highly desirable. Furthermore, a system that reduces banding in real time with faster processing than current systems would be highly desirable. A more accurate and efficient method for reducing banding would also be highly desirable. Furthermore, a method for reducing banding artifacts that is applicable to all B-mode applications would be highly desirable.